1. Field of Invention
The present invention relates to a piston-type compressor, in which fluid is compressed by means of reciprocating pistons connected to a swash plate. More particularly, it relates to a configuration of reciprocating pistons, which reduces the weight of the pistons in the refrigerator compressor for an automotive air conditioning system.
2. Description of the Related Art
Piston-type refrigerant compressors are typically used in air conditioning apparatuses for automobiles. A known piston-type refrigerant compressor is disclosed in U.S. Pat. No. 5,174,728 to Kimura et al. and in Japanese unexamined publication No. H9-105380, both of which are herein incorporated by reference in their entireties.
A description will be made with regard to a swash plate-type compressor as a reciprocating compressor. In the following description, and for convenience only, the left side of FIG. 1 will be referred to as the front side of the compressor while the right side thereof will be referred to as the rear side of the compressor.
Referring to FIG. 1, a compressor, which is generally designated by reference number 100, includes an annular casing forming closed cylinder housing 10. Closed cylinder housing 10 is provided with cylinder block 22, a hollow portion, such as a crank chamber 31, a front end plate 13, and a rear end plate 26. Pistons 11 are accommodated in cylinder bores 21 and reciprocate therein. Drive shaft 15, which is driven by an engine (not shown), is rotatably supported by means of the central portion of cylinder block 22 and front end plate 13. Rotor plate 14 is mounted on drive shaft 15, and synchronously rotates with drive shaft 15. Further, swash plate 20 is tiltably mounted on drive shaft 15, and is reciprocally slidable together with special sleeve 17, which is parallel to the axis of drive shaft 15. Rotor plate 14 and swash plate 20 are connected to each other by means of a hinge mechanism (not shown). Swash plate 20 engages the interior portion of the associated piston 11 along its circumference.
Cylinder block 22 is provided with communication passage 23, which allows crank chamber 31 to communicate with suction chamber 42. Communication passage 23 includes bellows 28, which opens and closes communication passage 23 according to a differential pressure and a suction pressure.
Control of the displacement of compressor 100 is achieved by varying the stroke of piston 11. The stroke of piston 11 varies in accordance with a difference between the pressures acting on the opposing sides of swash plate 20. A pressure difference is generated by balancing the pressure in crank chamber 31 acting on the rear surface of piston 11, and the suction pressure in cylinder bore 21 acting on the front surface of piston 11. The suction pressure acts on swash plate 20, through piston 11.
According to the above-described compressor 100, when drive shaft 15 rotates, rotor plate 14 rotates with drive shaft 15. The rotation of rotor plate 14 is transferred to swash plate 20 through hinge mechanism (not shown). Rotor plate 20 rotates with a surface inclined with respect to drive shaft 15, so that pistons 11 reciprocate in their respective cylinder bores 21. Therefore, refrigerant gas is drawn into suction chamber 42 and compressed, and then discharged from the inlet chamber into an associated discharge chamber 44.
Thus, the volume of compressed refrigerant gas discharged into discharge chamber 44 is regulated accordingly, as the pressure in crank chamber 31 is controlled so as to open and close communication passage 23 in relation to the differential pressure between the suction pressure and the preset pressure of bellows 28.
When the suction pressure is higher than the preset pressure of bellows 28, the communication passage 23 opens, the pressure in crank chamber 31 decreases, rotor plate 14 tilts to rotate with a greater angle with respect to drive shaft 15, and the stroke of piston 11 increases. As a result, the compression capacity of compressor 100 increases. On the other hand, when the suction pressure is other than the preset pressure of bellows 28, communication passage 23 closes, the pressure in crank chamber 31 increases, rotor plate 14 tilts to rotated with a smaller angle with respect to drive shaft 15, and the stroke of piston 11 increases. As a result, the compression capacity of compressor 100 decreases. Further, some of the refrigerant gas that remains in cylinder bore 21 is used as lubricating oil, which leaks into crank chamber 31 so as to lubricate the surface between rotor plate 14 and sleeves 17.
Referring to FIG. 2, piston 11 includes a cylindrical main body 12 which is sealingly formed with an open space (not shown) therein. Cylindrical main body 12 is provided with an annular groove 13 on the peripheral surface thereof for receiving a lubricating oil therein. Annular groove 13 is formed on a portion of piston 11 that is constantly located in cylinder bore 21 of cylinder block 22 during operation; thus, annular groove 13 does not enter crank chamber 31 even when piston 11 is located at bottom dead center of piston 11. Annular groove 13 includes three apertures 24, which communicate fluidly with open space 11a, at equal intervals.
Referring to FIGS. 3 and 4, piston 11 includes three second apertures 25, which are fluidly communicated with open space 11a, at equal intervals. Piston 11 includes first arm portion 16 axially extending from the one end of cylindrical main body 12, and integrally connected to the part of the peripheral surface of piston 11. Piston 11 also includes second arm portion 17 radially extending from one end of first arm portion 16. Piston 11 further includes a first shoe supporting portion 18. First shoe supporting portion 18 is formed on one axial end 11b of cylindrical main body 12. A second shoe supporting portion 19 is formed on one axial end of second arm portion 17 so as to face first shoe supporting portion 18. Each piston 11, which are manufactured as mentioned above, is slidably supported by sleeves 17, which are disposed in first shoe supporting portion 18 and second shoe supporting portion 19, and are inserted into and slidably disposed in cylinder bore 21.
When compressor 100 provided with piston 11 is activated, the rotary motion of drive shaft 15 is transmuted to swash plate 20 via rotor plate 14 and guide pins (not shown). Thus, each piston 11 reciprocates within its respective bore 21 so that suction gas is introduced into corresponding bore 21, then compressed and discharged as discharge gas into discharge chamber 44. Depending on a pressure differential between pressure in crank chamber 31 and suction chamber 42, the inclination of swash plate 20, and thus the stroke of piston 11, are changed to control the capacity of compressor 100 in a manner known in the art. The pressure in the crank chamber 31 is controlled by a control valve mechanism (not shown) provided in cylinder block 22 depending on the heat load.
According to the operation of compressor 100, cylinder bore 21 may be subjected to high pressure and low pressure conditions, alternatively. Due to the presence of first apertures 24 of piston 11, during the reciprocation of piston 11, first apertures 24 allow a breathing operation by permitting an alternate flow-in and flow-out of refrigerant gas between open space 11a and cylinder bore 21. A similar breathing operation is carried out to permit an alternate flow-in and flow-out of refrigerant gas between open space 11a and crank chamber 31 through second apertures 25 to thereby assist a smooth breathing operation between open space 11a and crank chamber 31.
Lubricating oil included in refrigerant gas adheres to inner surface of cylinder bore 21. As it reciprocates, annular groove 13 scrapes and catches lubricating oil on the inner surface of cylinder bore 21. Therefore, highly condensed refrigerant gas flows into open space 11a and crank chamber 31. Some of the refrigerant gas is effectively used as lubricating oil, which lubricates the sliding surface between rotor plate 14 and sleeves 17 in crank chamber 31.
Although piston 11 requires open space 11a formed therein, and for cylindrical main body 12 to have a thin thickness in order to reduce the weight of the piston 11, it is desirable to provide a lighter weight piston in the compressor used in an automobile.
Generally, a pair of members for piston are assembled to a piston by welding in a vacuum. According to this manufacturing process, each piston has to be manufactured in a complex manner in vacuums, since a pair of members forming piston 11 are welded in a vacuum after being connected to each other.